Self-wetting adhesive composition

ABSTRACT

A self-wetting adhesive composition is described comprising the reaction product of a low T g  (meth)acrylate solute copolymer component; a low T g  solvent monomer solvent monomer component comprising low T g  monomers, a multifunctional acrylate; and a polymerizable siloxane copolymer having at least one polydiorganosiloxane segment and at least on oxyalkylene segment.

BACKGROUND

Pressure-sensitive tapes are virtually ubiquitous in the home andworkplace. In its simplest configuration, a pressure-sensitive tapecomprises an adhesive and a backing, and the overall construction istacky at the use temperature and adheres to a variety of substratesusing only moderate pressure to form the bond. In this fashion,pressure-sensitive tapes constitute a complete, self-contained bondingsystem.

According to the Pressure-Sensitive Tape Council, adhesives are known topossess properties including the following: (1) adherence with no morethan finger pressure, (2) sufficient ability to hold onto an adherend,and (3) sufficient cohesive strength to be removed cleanly from theadherend. Materials that have been found to function well as ADHESIVEsinclude polymers designed and formulated to exhibit the requisiteviscoelastic properties resulting in a desired balance of tack, peeladhesion, and shear holding power. These requirements are assessedgenerally by means of tests which are designed to individually measuretack, adhesion (peel strength), and cohesion (shear holding power), asnoted in A.V. Pocius in Adhesion and Adhesives Technology: AnIntroduction, 2^(nd) Ed., Hanser Gardner Publication, Cincinnati, Ohio,2002. These measurements taken together constitute the balance ofproperties often used to characterize an adhesive.

SUMMARY

The present disclosure provides novel adhesive compositions comprising ahighly crosslinked low T_(g) (meth)acrylic (co)polymer and a siloxanecopolymer having at least one polydiorganosiloxane segment and at leaston oxyalkylene segment (“siloxane copolymer”).

The adhesives of this disclosure provide the desired balance of tack,peel adhesion, and shear holding power, and further conform to theDahlquist criteria; i.e. the modulus of the adhesive at the applicationtemperature, typically room temperature, is less than 3×10⁶ dynes/cm ata frequency of 1 Hz. The adhesives of the present disclosure areparticularly useful for forming strong bonds to low surface energy (LSE)substrates, and further exhibit exceptional adhesion at elevatedtemperatures on these substrates.

The cured adhesive composition, when cured, exhibit low peel strengthand are self-wetting. By “self-wetting” is meant that the cured adhesiveformulation exhibits spontaneous wetting out on a smooth surface towhich it is applied with little or no external pressure. An additionalcharacteristic of a self-wetting adhesive formulation is that the curedadhesive is removable with little or no residue remaining on the surfaceto which it had been applied. The initial 180° peel strength of thecured formulation is less than about 5 N/dm and in some cases less thanabout 1 N/dm.

The adhesive compositions, when cured, is non-yellowing, exhibits lowshrinkage, low birefringence and low sensitivity to moisture (cloudpoint-resistant), making it suitable for many optical applicationsincluding, but not limited to bonding polarizers to modules of a liquidcrystal display (LCD) and attaching various optical films to a glasslens in, for example, mobile hand held (MHH) devices.

In some embodiments the adhesives adhere, yet remain repeatedly peelablefrom a variety of smooth substrates such as glass, metal, wood, paperwith matte or glossy finish surfaces or polymer substrates over a longperiod of time without damaging the substrate or leaving any adhesiveresidue or stain on the surface. Adhesive articles are providedcomprising a flexible backing such as, for example, a biaxially-orientedpolyethylene terephthalate.

Ideally, depending on the substrate, the removable adhesive must providewettability to the substrate and quick initial adhesion (sufficientinitial tack or quick stick) to quickly fix the adhesive to the desiredsubstrate. On the other hand, the adhesive should exhibit only a low andat any rate acceptable adhesion buildup with time, even at elevatedtemperatures, to ensure clean peelability after a prolonged dwell. Theadhesive should furthermore be characterized by an adequate peelstrength to give a reliable, high performance adhesion to the substratewithout damaging the substrate when removing the adhesive. The adhesivesexhibit sufficient cohesive and tensile strength and hence form anddimensional stability of the adhesive article to allow proper handlingand, in particular, the reapplication of the article to substrate afterhaving peeled it off once or several times. A sufficient cohesivestrength is also desirable in order to limit the cold flow of theadhesive on a surface, a process which leads to an undesirable build-upof peel strength over time. The static shear strength should be highenough to allow light-duty mounting applications without being too highto result in permanent adhesion. In some embodiments the adhesive shouldfurthermore exhibit a high resistivity against water in order to allowoutdoor applications. Furthermore, a high resistance against organicsolvents is desirable.

In some embodiments the adhesive are transparent for visible light inorder to allow for an essentially invisible mounting of objects ontransparent substrates such as glass or transparent polymers. Thepresent disclose provides an optically clear adhesive article thatincludes an optically clear and the cured optical adhesive compositiondisposed on a major surface of the substrate. This disclosure furtherprovides and optical clear article comprise a first and second opticalclear substrate, and the cured adhesive disposed between the twosubstrates. The articles of the disclosure may have a thickness greaterthan about 0.03 millimeters, generally a birefringence (absolute) ofless than 1×10⁻⁶, light transmission greater than about 85% (over thespectral region of interest), preferably greater than 90%, morepreferably greater than 95%, and a CIELAB b* less than about 1.5 units,preferably less than about 1.0 unit for samples with adhesive thicknessof 500 microns.

Exemplary formulations can also easily be removed, so that when used forscreen protection for example, a film covering can be removed, should aconsumer desire to do so or if other circumstances warrant, withoutdamaging the screen or leaving behind a residue. Exemplary formulationsalso exhibit a low peel strength upon curing resulting an adhesive thatis easily removable.

DETAILED DESCRIPTION

The adhesive compositions of this disclosure comprise, in part, a lowT_(g) copolymer component, comprising a low T_(g) monomer and optionalacid-functional monomer. The T_(g) of the copolymer is ≦0° C.,preferably ≦−20° C., most preferably <-50° C. .

The (meth)acrylate ester monomer useful in preparing the low T_(g)(meth)acrylate (co)polymer is a monomeric (meth)acrylic ester of anon-tertiary alcohol, which alcohol contains from 1 to 18 carbon atomsand preferably an average of from 4 to 12 carbon atoms. A mixture ofsuch monomers may be used.

Examples of monomers suitable for use as the (meth)acrylate estermonomer include the esters of either acrylic acid or methacrylic acidwith non-tertiary alcohols such as ethanol, 1-propanol, 2-propanol,1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-hexanol,2-methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 1-octanol, 2-octanol,isooctylalcohol, 2-ethyl-1-hexanol, 1-decanol, 2-propylheptanol,1-dodecanol, 1-tridecanol, 1-tetradecanol, citronellol,dihydrocitronellol, and the like. In some embodiments, the preferred(meth)acrylate ester monomer is the ester of (meth)acrylic acid withbutyl alcohol or isooctyl alcohol, or a combination thereof, althoughcombinations of two or more different (meth)acrylate ester monomer aresuitable.

In some embodiments, the preferred (meth)acrylate ester monomer is theester of (meth)acrylic acid with an alcohol derived from a renewablesource, such as 2-octanol, citronellol, dihydrocitronellol.

In some embodiments a portion of the above described (meth)acrylateesters may be substituted with (meth)acrylates derived from 2-alkylalkanols (Guerbet alcohols) as described in U.S. Pat. No. 8,137,807(Lewandowski et al.), incorporated herein by reference.

The low T_(g) (meth)acrylate ester monomer is present in an amount of 90to 100 parts, preferably 95 to 100 partsby weight based on 100 partstotal monomer content used to prepare the low T_(g) copolymer.Preferably (meth)acrylate ester monomer is present in an amount of 95 to99 parts by weight based on 100 parts total monomer content of the lowT_(g) copolymer.

The polymer may further comprise an acid functional monomer, where theacid functional group may be an acid per se, such as a carboxylic acid,or a portion may be salt thereof, such as an alkali metal carboxylate.Useful acid functional monomers include, but are not limited to, thoseselected from ethylenically unsaturated carboxylic acids, ethylenicallyunsaturated sulfonic acids, ethylenically unsaturated phosphonic acids,and mixtures thereof. Examples of such compounds include those selectedfrom acrylic acid, methacrylic acid, itaconic acid, fumaric acid,crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl(meth)acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid,2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, andmixtures thereof

Due to their availability, acid functional monomers of the acidfunctional copolymer are generally selected from ethylenicallyunsaturated carboxylic acids, i.e. (meth)acrylic acids. When evenstronger acids are desired, acidic monomers include the ethylenicallyunsaturated sulfonic acids and ethylenically unsaturated phosphonicacids. The acid functional monomer, when present, is generally used inamounts of 0.5 to 5 parts by weight, based on 100 parts by weight totalmonomer of the low T_(g) copolymer.

In addition to the low T_(g) monomer and acid functional monomer, thecopolymer may optional include other monomers, such as non-acidfunctional polar monomers, vinyl monomers and vinyl ether monomers,provided the resultant copolymers has a Tg of <0° C., maintains thecompatibility with the siloxane copolymer, and has the requisite opticaland adhesive properties. Such additional monomers may be used in amountsof up to 5 parts by weight, relative to 100 parts by weight of totalmonomers.

Representative examples of suitable polar monomers include but are notlimited to 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone;N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl substitutedacrylamide; t-butyl acrylamide; dimethylaminoethyl acrylamide; N-octylacrylamide; poly(alkoxyalkyl) (meth)acrylates including2-(2-ethoxyethoxy) ethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate,2-methoxyethoxyethyl (meth)acrylate, 2-methoxyethyl methacrylate,polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers, includingvinyl methyl ether; and mixtures thereof. Preferred polar monomersinclude those selected from the group consisting of 2-hydroxyethyl(meth)acrylate and N-vinylpyrrolidinone.

A useful predictor of interpolymer T_(g) for specific combinations ofvarious monomers can be computed by application of Fox Equation:1/T_(g)=ΣWi/T_(g)i. In this equation, T_(g) is the glass transitiontemperature of the mixture, Wi is the weight fraction of component i inthe mixture, and T_(g)i is the glass transition temperature of componenti, and all glass transition temperatures are calculated in Kelvin (K).As used herein the term “low T_(g) monomer” refers to a monomer, whichwhen homopolymerized, produce a (meth)acrylate copolymer having a T_(g)of ≦20° C., preferably ≦0° C., more preferably ≦−20° C., as calculatedusing the Fox Equation. Alternatively, the glass transition temperaturecan be measured in a variety of known ways, including, e.g., throughdifferential scanning calorimetry (DSC).

In order to provide sufficient cohesive strength of the adhesivecomposition, a multifunctional (meth)acrylate is incorporated into theblend of polymerizable monomers. A multifunctional (meth)acrylate, whenused in the amounts described herein provide an adhesive having lowtack, high shear modulus, low peel, and facilitates the self-wettingproperty. Examples of useful multifunctional (meth)acrylate include, butare not limited to, di(meth)acrylates, tri(meth)acrylates, andtetra(meth)acrylates, such as 1,6-hexanediol di(meth)acrylate,poly(ethylene glycol) di(meth)acrylates, polybutadiene di(meth)acrylate,polyurethane di(meth)acrylates, and propoxylated glycerintri(meth)acrylate, and mixtures thereof. The amount and identity ofmultifunctional (meth)acrylate is tailored depending upon application ofthe adhesive composition.

Typically, the multifunctional (meth)acrylate is present in amountsgreater than 5 parts based on 100 parts of the low T_(g) solutecopolymer and solvent monomer component. More specifically, themultifunctional (meth)acrylate may be present in amounts from 5 to 50parts, preferably at least 10 parts, based on 100 parts of the low T_(g)solute copolymer and solvent monomer component.

The curable composition further comprises a free radically polymerizablesegmented siloxane-based copolymer. A wide range of free radicallypolymerizable segmented siloxane-based copolymers are suitable for thisapplication. Typically, the free radically polymerizable segmentedsiloxane-based copolymer comprises a segmented siloxane-based copolymerwith at least one free radically polymerizable (meth)acrylate group.

One suitable class of free radically polymerizable segmentedsiloxane-based copolymers are so called “silicone -polyether” blockcopolymer-based free radically polymerizable copolymers. Thesecopolymers typically have at least one siloxane block (i.e. withdiorgano including dialkyl or diaryl siloxane (—SiR'₂O—) repeatingunits), and at least one polyether or (poly)oxyalkylene block.Frequently the silicone-polyether block copolymer-based free radicallypolymerizable copolymers have at least two free radically polymerizablegroups. Some silicone-polyether block copolymer-based free radicallypolymerizable copolymers have more than two free radically polymerizablegroups.

The block copolymers may be linear having a general structure of thetype:

X—(R²—O)_(a)—Q—(SiR¹ ₂O)_(b)—Q—(O—R²)_(a)—X

where X is H is a free radically polymerizable group (including vinyl,allyl and preferably a (meth)acrylate group; R² is an alkylene group andtypically is an ethylene group (—CH₂—CH₂—); Q is difunctional linkinggroup, typically an alkylene group such as a propylene group(—CH₂—CH₂—CH₂—); R¹ is alkyl or aryl group, typically a methyl group;and a and b are independently integers greater than 1, with the provisothat at least one X is a a free radically polymerizable group.

Other block copolymers have pendent structures of the general type:

R¹ ₃SiO—(SiR¹ ₂O)_(b)—(SiR¹(—Q(—O—R²)_(a)—X)O)_(a)SiR¹ ₃

where R¹ is alkyl or aryl group, typically a methyl group; X is a freeradically polymerizable group as described above; R² is an alkylenegroup and typically is an ethylene group (—CH₂—CH₂—); Q is adifunctional linking group, typically an alkylene group such as apropylene group (—CH₂—CH₂—CH₂—); and a and b are independently integersgreater than 1.

Some useful free radically polymerizable segmented siloxane-basedcopolymers are silicone additives that are commercially available as“slip agents”. It was unexpected that agents that are marketed as slipagents would improve the self-wetting performance and that couldfree-radically polymerized into the adhesive (co)polymer chain. Examplesof silicone additives that are useful free radically polymerizablesegmented siloxane-based copolymers include: those from MomentivePerformance Materials, Columbus, OH, under the trade name “COAT-O-SIL”such as COAT-O-SIL 3503 and COAT-O-SIL 3509; those from CytecIndustries, Inc., Woodland Park, N.J., under the trade name “EBECRYL”such as EBECRYL 350 and EBECRYL 1360; and TEGORAD 2200N commerciallyavailable from Evonik Industries, AG, Essen, Germany.

The amount of siloxane copolymer used depends on the materialscomprising the substrates and polymeric film, as well as theirdimensions. Generally, the amount of siloxane copolymer used is greaterthan 5 parts by weight, relative to 100 parts by weight of the solute(co)polymer and solvent monomers (the syrup polymer composition), orrelative to cured acrylic copolymer. Preferably the amount of siloxanecopolymer is from 5 to 50 parts by weight relative to 100 parts byweight of the syrup polymer composition, or relative to cured acryliccopolymer to provide useful bonding times and faster wet-out of asubstrate.

The curable composition is preferably prepared by a syrup polymerizationtechnique. “Syrup polymer composition” refers to a solution of a solute(co)polymer in one or more solvent monomers, the composition having aviscosity of from 500 to 10,000 cPs at 22° C. Here, a monomer mixtureconsisting of the (meth) acrylate monomer, the optional acid functionalmonomer and other monomers are combined and partially polymerized usinga thermal- or photoinitiator. The resulting syrup polymer, comprising asolute (meth)acrylate copolymer and unreacted solvent monomers, is thencombined with the multiacrylate crosslinking agent and photoinitiator.If desired, additional solvent monomers and initiators may be addedafter the initial partial polymerization In the presence of aphotoinitiator, subsequent treatment with UV radiation willsimultaneously polymerize the solvent monomers and crosslink thecomposition with the multiacrylate.

Any conventional free radical initiator may be used to generate theinitial polymerization to form the syrup polymer composition. Examplesof suitable thermal initiators include peroxides such as benzoylperoxide, dibenzoyl peroxide, dilauryl peroxide, cyclohexane peroxide,methyl ethyl ketone peroxide, hydroperoxides, e.g., tert-butylhydroperoxide and cumene hydroperoxide, dicyclohexyl peroxydicarbonate,2,2,-azo-bis (isobutyronitrile), and t-butyl perbenzoate. Examples ofcommercially available thermal initiators include initiators availablefrom DuPont Specialty Chemical (Wilmington, Del.) under the VAZO tradedesignation including VAZO™67 (2,2′-azo-bis (2-methybutyronitrile))VAZO™64 (2,2′-azo-bis(isobutyronitrile)) and VAZO™52(2,2′-azo-bis(2,2-dimethyvaleronitrile)), and Lucidol™70 from ElfAtochem North America, Philadelphia, Pa.

The solute (co)polymer(s) may be prepared conventionally in anon-monomeric solvent and advanced to high conversion (degree ofpolymerization). When solvent (monomeric or non-monomeric) is used, thesolvent may be removed (for example by vacuum distillation) eitherbefore or after formation of the syrup polymer. While an acceptablemethod, this procedure involving a highly converted functional polymeris not preferred because an additional solvent removal step is required,another material may be required (the non-monomeric solvent), anddissolution of the high molecular weight, highly converted solutepolymer in the monomer mixture may require a significant period of time.Additional solvent monomers may be added to the syrup polymercomposition to reduce the viscosity as desired.

A preferred method of preparation of the coatable syrup polymer isphotoinitiated free radical polymerization. Advantages of thephotopolymerization method are that 1) heating the monomer solution isunnecessary and 2) photoinitiation is stopped completely when theactivating light source is turned off. Polymerization to achieve acoatable viscosity may be conducted such that the conversion of monomersto polymer is up to about 30%. Polymerization can be terminated when thedesired conversion and viscosity have been achieved by removing thelight source and by bubbling air (oxygen) into the solution to quenchpropagating free radicals.

The monomer mixture is generally partially polymerized (converted) toproduce a the syrup copolymer comprising up to 30 parts by weight of thesolute copolymer in solvent monomers and has a viscosity of from 500 to10,000 cPs at 22° C. After partial conversion, the multifunctionalacrylate, the siloxane copolymer and optional additional monomers areadded and the syrup polymer composition further polymerized, preferablyby photopolymerization using a photoinitiator.

Useful photoinitiators include benzoin ethers such as benzoin methylether and benzoin isopropyl ether; substituted acetophenones such as 2,2-dimethoxyacetophenone, available as Irgacure™651 photoinitiator (CibaSpecialty Chemicals), or as Esacure™KB-1 photoinitiator (Sartomer Co.;West Chester, Pa.), and dimethoxyhydroxyacetophenone; substituteda-ketols such as 2-methyl-2-hydroxy propiophenone; aromatic sulfonylchlorides such as 2-naphthalene-sulfonyl chloride; and photoactiveoximes such as 1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime.Particularly preferred among these are the substituted acetophenones.Preferred photoinitiators are photoactive compounds that undergo aNorrish I cleavage to generate free radicals that can initiate byaddition to the acrylic double bonds. Additional photoinitiator can beadded to the mixture to be coated after the copolymer has been formed,i.e., photoinitiator can be added to the syrup polymer mixture.

The syrup polymer composition and the photoinitiator may be irradiatedwith activating UV radiation to polymerize the monomer component(s). UVlight sources can be of two types: 1) relatively low light intensitysources such as backlights which provide generally 10 mW/cm² or less (asmeasured in accordance with procedures approved by the United StatesNational Institute of Standards and Technology as, for example, with aUvimap™ UM 365 L-S radiometer manufactured by Electronic Instrumentation& Technology, Inc., in Sterling, VA) over a wavelength range of 280 to400 nanometers and 2) relatively high light intensity sources such asmedium pressure mercury lamps which provide intensities generallygreater than 10 mW/cm², preferably between 15 and 450 mW/cm². Whereactinic radiation is used to fully or partially polymerize the syruppolymer composition, high intensities and short exposure times arepreferred. For example, an intensity of 600 mW/cm² and an exposure timeof about 1 second may be used successfully. Intensities can range fromabout 0.1 to about 150 mW/cm², preferably from about 0.5 to about 100mW/cm², and more preferably from about 0.5 to about 50 mW/cm². Suchphotoinitiators preferably are present in an amount of from 0.1 to 1.0pbw per 100 pbw of the syrup polymer composition.

The degree of conversion (of monomers to copolymer) can be monitoredduring the irradiation by measuring the index of refraction of thepolymerizing. Useful coating viscosities are achieved with conversions(i.e. the percentage of available monomer polymerized) in the range ofup to 30%, preferably 2-20%, more preferably from 5-15%, and mostpreferably from 7-12%. The molecular weight (weight average) of thesolute polymer(s) is at least 100,000, preferably at least 250,000, morepreferably at least 500,000.

It will be understood that a syrup polymerization method will produce a“dead polymer” in the initial free radical polymerization; i.e. a fullypolymerized, not free-radically polymerizable polymer. Subsequently thesolvent monomers do not free-radically polymerize onto the extant solutecopolymer. Upon compounding the syrup polymer, further exposure to UVinitiates free radical polymerization of the solvent monomers andmultiacrylate crosslinking agent to produce a distinct crosslinkedcopolymer. Upon curing, the product may be characterized as a homogenousmixture of a) a low T_(g) (co)polymer (from the initial polymerization,b) a highly crosslinked low T_(g) (co)polymer (from the subsequentpolymerization of the monomer and multiacrylate component and c) thesiloxane copolymer.

The syrup method provides advantages over solvent or solutionpolymerization methods; the syrup method yielding higher molecularweights. These higher molecular weights increase the amount of chainentanglements, thus increasing cohesive strength.

The syrup polymer composition may comprise:

-   -   a) 5 to 40 parts, preferably 10 to 40 parts by weight of a low        T_(g) (meth)acrylate solute (co)polymer component;    -   b) 60 to 95, preferably 60 to 90, parts by weight of a low T_(g)        solvent monomer solvent monomer component comprising low T_(g)        monomers and a multifunctional acrylate, the sum of a) and b)        being 100 parts by weight;    -   c) 5 to 50 parts by weight a plasticizer, relative to 100        parts a) and b).

The thermal and photoinitiators can be employed in concentrationsranging from about 0.0001 to about 3.0 pbw, preferably from about 0.001to about 1.0 pbw, and more preferably from about 0.005 to about 0.5 pbw,per 100 pbw of the monomers.

The adhesive may be prepared by the steps of

-   -   1) free radically polymerizing a mixture of the low T_(g)        monomer and optional acid-functional and other monomers monomer        to produce a syrup polymer composition such that the conversion        of monomers to polymer is up to about 30%,    -   2) adding the multifunctional acrylate crosslinking agent,        siloxane copolymer, optional additional monomers and        photoinitiator to the syrup polymer composition, and    -   3) further polymerizing the mixture, preferably by        photopolymerization.

If desired, the syrup polymer composition may be coated on a substrateprior to further polymerization.

In some embodiments the charge of additional monomers in step 2) isdesirable. Such additional monomers may further reduce the viscosity ofthe syrup polymer. Further, it has been found desirable to add the acidfunctional monomers and/or non-acid functional polar monomers in step)to avoid peel adhesion build on substrates. If a second charge ofadditional monomers is used, up to 70 parts by weight, preferably up to50 parts by weight of monomers may be reserved from the initial monomercharge for the second monomer charge in step 2). Thus the initialmonomer charge may comprise 30 parts or less in the initial charge, themixture is partially polymerized to a syrup polymer composition, andthen up to 70 parts of additional monomers are added in the secondcharge.

Those skilled in the art will also know that other additives such asfillers, antioxidants, stabilizers, and colorants may be blended withthe adhesive for beneficial properties.

In some embodiments the composition may include filler. In manyembodiments the filler is of a type and used in amounts such thatincorporation does not deleterious affect the optical and adhesiveproperties of the adhesive. In some embodiments, small amounts of fillermay be used to improve the cohesive strength of the adhesive.

Such compositions may include at least 1 wt-%, more preferably at least5 wt-%, and most preferably at least 10 wt-% filler, based on the totalweight of the syrup polymer composition. In some embodiments the totalamount of filler is at most 50 wt-%, preferably at most 40 wt-%, andmore preferably at most 30 wt-% filler.

Fillers may be selected from one or more of a wide variety of materials,as known in the art, and include organic and inorganic filler. Inorganicfiller particles include silica, submicron silica, zirconia, submicronzirconia, and non-vitreous microparticles of the type described in U.S.Pat. No. 4,503,169 (Randklev).

Filler components include nanosized silica particles, nanosized metaloxide particles, and combinations thereof. Nanofillers are alsodescribed in U.S. Pat. Nos. 7,090,721 (Craig et al.), 7,090,722 (Budd etal.), 7,156,911 (Kangas et al.), and 7,649,029 (Kolb et al.).

In some embodiments, the composition preferably comprise a nanoparticlefiller having an average primary particle size of less than about 100nanometers, preferably less than 50 nanometers, and more preferably lessthan 10 nanometers. As used herein, the term “primary particle size”refers to the size of a non-associated single particle. The typicallyhas an average primary particle size of at least about 1 nanometers(nm), and preferably at least about 5 nm. The average surface area ofsuch a filler is preferably at least about 20 square meters per gram(m²/g), more preferably, at least about 50 m²/g, and most preferably, atleast about 100 m²/g.

In some embodiments, a surface modified filler can be used. The surfacemodifying agents for the fillers may enhance dispersibility orrheological properties. Examples of silanes of this type include, forexample, aryl polyethers, alkyl, hydroxy alkyl, hydroxy aryl, or aminoalkyl functional silanes.

In many embodiments, a preferred filler is hydrophobic fumed silica,such as Aerosil™ R972 fumed silica from Degussa.

The resulting adhesives are self wetting and removable. The adhesivesexhibit great conformability permitting them to spontaneously wet outsubstrates. The surface characteristics also permit the adhesives to bebonded and removed from the substrate repeatedly for repositioning orreworking. The strong cohesive strength of the adhesives gives themstructural integrity limiting cold flow and giving elevated temperatureresistance in addition to permanent removability. In some embodimentsthe initial removability of an adhesive coated article bonded to a glasssubstrate, as measured by the 180° Peel Adhesion test described in theExamples section below, is no greater than 5 Newtons/decimeter. Uponaging for one week at room temperature the removability, as measured bythe 180° Peel Adhesion test is no more than 10 Newtons/decimeter. Inother embodiments, the removability after aging for at least one week atroom temperature, as measured by the 180° Peel Adhesion is no more than5 N/dm.

Adhesive articles may be prepared by coating the adhesive orpre-adhesive composition on a suitable support, such as a flexiblebacking Examples of materials that can be included in the flexiblebacking include polyolefins such as polyethylene, polypropylene(including isotactic polypropylene), polystyrene, polyester, polyvinylalcohol, poly(ethylene terephthalate), poly(butylene terephthalate),poly(caprolactam), poly(vinylidene fluoride), polylactides, celluloseacetate, and ethyl cellulose and the like. Commercially availablebacking materials useful in the invention include kraft paper (availablefrom Monadnock Paper, Inc.); cellophane (available from Flexel Corp.);spun-bond poly(ethylene) and poly(propylene), such as Tyvek™ and Typar™(available from DuPont, Inc.); and porous films obtained frompoly(ethylene) and poly(propylene), such as Teslin™ (available from PPGIndustries, Inc.), and Cellguard™ (available from Hoechst-Celanese).

The backing may also be formed of metal, metalized polymer films, orceramic sheet materials may take the form of any article conventionallyknown to be utilized with pressure sensitive adhesive compositions suchas labels, tapes, signs, covers, marking indicia, and the like.

The above-described compositions are coated on a substrate usingconventional coating techniques modified as appropriate to theparticular substrate. For example, these compositions can be applied toa variety of solid substrates by methods such as roller coating, flowcoating, dip coating, spin coating, spray coating knife coating, and diecoating. These various methods of coating allow the compositions to beplaced on the substrate at variable thicknesses thus allowing a widerrange of use of the compositions. Coating thicknesses may vary, butcoating thicknesses of 2-500 microns (dry thickness), preferably about25 to 250 microns, are contemplated.

In some preferred embodiments, the partially cured composition, i.e. thesolute (co)polymer, unreacted monomers, multiacrylate crosslinking agentand siloxane copolymer is coated on a backing or release liner, and thenfurther polymerized.

The substrate is selected depending on the particular application inwhich it is to be used. For example, the adhesive can be applied tosheeting products, (e.g., decorative graphics and reflective products),label stock, and tape backings Additionally, the adhesive may be applieddirectly onto a substrate such as an automotive panel, or a glass windowso that another substrate or object can be attached to the panel orwindow.

The adhesive can also be provided in the form of an adhesive transfertape in which at least one layer of the adhesive is disposed on arelease liner for application to a permanent substrate at a later time.The adhesive can also be provided as a single coated or double coatedtape in which the adhesive is disposed on a permanent backing

Exemplary adhesive articles in which the self wetting and removabilityfeatures are especially important include, for example: large formatarticles such as graphic articles and protective films; and informationdisplay devices.

Large-format graphic articles or protective films typically include athin polymeric film backed by an adhesive. These articles may bedifficult to handle and apply onto a surface of a substrate. The largeformat article may be applied onto the surface of a substrate by what issometimes called a “wet” application process. The wet applicationprocess involves spraying a liquid, typically a water/surfactantsolution, onto the adhesive side of the large format article, andoptionally onto the substrate surface. T he liquid temporarily“detackifies” the adhesive so the installer may handle, slide, andre-position the large format article into a desired position on thesubstrate surface. The liquid also allows the installer to pull thelarge format article apart if it sticks to itself or prematurely adheresto the surface of the substrate. Applying a liquid to the adhesive mayalso improve the appearance of the installed large format article byproviding a smooth, bubble free appearance with good adhesion build onthe surface of the substrate.

Examples of a large format protective films include window films such assolar control films, shatter protection films, decoration films and thelike. In some instances the film may be a multilayer film such as amultilayer IR film (i.e., an infrared reflecting film), such as amicrolayer film having selective transmissivity such as an opticallyclear but infrared reflecting film as described in U.S. Pat. No.5,360,659 (Arends et al.).

While the wet application process has been used successfully in manyinstances, it is a time consuming and messy process. A “dry” applicationprocess is generally desirable for installing large format graphicarticles. Adhesives that are self wetting and removable may be appliedwith a dry installation process. The articles are easily attached to alarge substrate because they are self wetting and yet they may be easilyremoved and repositioned as needed.

In other applications, such as information display devices, the wetapplication process cannot be used. Examples of information displaydevices include devices with a wide range of display area configurationsincluding liquid crystal displays, plasma displays, front and rearprojection displays, cathode ray tubes and signage. Such display areaconfigurations can be employed in a variety of portable and non-portableinformation display devices including personal digital assistants, cellphones, touch-sensitive screens, wrist watches, car navigation systems,global positioning systems, depth finders, calculators, electronicbooks, CD or DVD players, projection television screens, computermonitors, notebook computer displays, instrument gauges, instrumentpanel covers, signage such as graphic displays (including indoor andoutdoor graphics, bumper stickers, etc) reflective sheeting and thelike.

A wide variety of information display devices are in use, bothilluminated devices and non-illuminated devices. Many of these devicesutilize adhesive articles, such as adhesive coated films, as part oftheir construction. One adhesive article frequently used in informationdisplay devices is a protective film. Such films are frequently used oninformation display devices that are frequently handled or have exposedviewing surfaces.

In some embodiments, the adhesives of this disclosure may be used toattach such films to information display devices because the adhesiveshave the properties of optical clarity, self wetting and removability.The adhesive property of optical clarity permits the information to beviewed through the adhesive without interference. The features of selfwetting and removability permit the film to be easily applied to displaysurface, removed and reworked if needed during assembly and also removedand replaced during the working life of the information display device.

The articles of the disclosure may have a thickness greater than about0.03 millimeters, generally a birefringence (absolute) of less than1×10⁻⁶, light transmission greater than about 85% (over the spectralregion of interest), preferably greater than 90%, more preferablygreater than 95%, and a CIELAB b* less than about 1.5 units, preferablyless than about 1.0 unit for samples with adhesive thickness of 500microns. Further, the adhesive layer of these articles permeably haveoptical properties at least equal to those of the article.

Generally, the optical properties of the adhesive layer per se ismeasured indirectly by measuring the optical properties of the article(substrate coated with adhesive) and the substrate alone. The opticalproperties, such as transmissivity are generally reported as an averageover the spectral region of interest; UV, visible and IR. Therefore, theadhesives of this disclosure have a birefringence (absolute) of lessthan 1×10⁻⁶, light transmission greater than about 85% (over thespectral region of interest), preferably greater than 90%, morepreferably greater than 95%, and a CIELAB b* less than about 1.5 units,preferably less than about 1.0 unit, over the spectral regions ofinterest.

In some embodiments this disclosure provides solar control articles thatmay be applied to windows to reduce the transmissivity over the spectralregion of interest including UV, visible and IR. The solar controlarticles comprise a solar control film and a layer of the adhesive ofthis disclosure on a major surface thereof

Solar control films are known and include dyed and vacuum-coatedpolymeric films reduce the transmissivity of various spectral regionfrom the incident light, i.e. sunlight. To reduce heat load fromincident light, solar transmission is blocked in either the visible orthe infrared portions of the solar spectrum (i.e., at wavelengthsranging from 400 nm to 2500 nm or greater.) Primarily throughabsorption, dyed films can control the transmission of visible light andconsequently provides glare reduction. However, dyed films generally donot block near-infrared solar energy and consequently are not completelyeffective as solar control films. Other known window films arefabricated using vacuum-deposited grey metals, such as stainless steel,inconel, monel, chrome, or nichrome alloys. The deposited grey metalfilms offer about the same degrees of transmission in the visible andinfrared portions of the solar spectrum. The grey metal films arerelatively stable when exposed to light, oxygen, and/or moisture, and inthose cases in which the transmission of the coatings increases due tooxidation, color changes are generally not detectable. After applicationto clear glass, grey metals block light transmission by approximatelyequal amounts of solar reflection and absorption. Vacuum-depositedlayers such as silver, aluminum, and copper control solar radiationprimarily by reflection and are useful only in a limited number ofapplications due to the high level of visible reflectance. A modestdegree of selectivity (i.e., higher visible transmission than infraredtransmission) is afforded by certain reflective materials, such ascopper and silver.

More recently, solar control films based on multilayer optical films(MLOF) have been developed which comprise hundreds or even thousands offilm layers and optional nanoparticles, and which selectively transmitor reflect based on small differences in the refractive indices ofadjacent film layers and reflectance or absorbance of the nanoparticles.The film layers have different refractive index characteristics so thatsome light is reflected at interfaces between adjacent layers. Thelayers are sufficiently thin so that light reflected at a plurality ofthe interfaces undergoes constructive or destructive interference inorder to give the film the desired reflective or transmissiveproperties. For optical films designed to reflect light at ultraviolet,visible, or near-infrared wavelengths, each layer generally has anoptical thickness (i.e., a physical thickness multiplied by refractiveindex) of less than about 1 micrometer. Thicker layers can, however,also be included, such as skin layers at the outer surfaces of the film,or protective boundary layers disposed within the film that separatepackets of layers.

One such solar control multilayer film is described in US2006154049(Weber et al., incorporated herein by reference) which describes amultilayer film article including an infrared light reflectingmultilayer film having alternating layers of a first polymer type and asecond polymer type, an infrared light absorbing nanoparticle layerincluding a plurality of metal oxide nanoparticles dispersed in a curedpolymeric binder and having a thickness in a range from 1 to 20micrometers. The nanoparticle layer being disposed adjacent themultilayer film.

Other useful solar control films include those described in EP 355962(Gilbert), U.S. Pat. No. 3,290,203 (Antonson et al.), U.S. Pat. No.3,681,179 (Theissen), U.S. Pat. No. 4,095,013 (Burger), U.S. Pat. No.6,565,992 (Ouderkirk et al.), U.S. Pat. No. 5,227,185 (Gobran), U.S.Pat. No. 4,329,396 (Arriban et al.), U.S. Pat. No. 7,368,161 (McGurranet al.), U.S. Pat. No. 6,811,867 (McGurran et al.), U.S. Pat. No.7,906,202 (Padiyath et al.) and U.S. Pat. No. 6,040,061 (Bland et al.),incorporated herein by reference.

Examples

Materials. Commercial reagents were used as received. When notspecified, reagents were obtained from Sigma Aldrich.

-   -   2-OA-2-octyl acrylate    -   HDDA—hexanediol diacrylate    -   IOA—isooctyl acrylate    -   Coatosil—Coatosil™ 3509 (an acrylated silicone polyether        copolymer from Momentive, Columbus, Ohio)

Test Methods 180° Peel Adhesion Test (Peel)

A test sample was prepared by placing a 0.5 (12.2 cm) inch wide by 7inch (178 cm) long adhesive coated tape on a 100 cm by 250 cm glass orstainless steel plates, as specified in the examples. The plates werecleaned by wiping with isopropanol before testing. The tape was rolleddown onto the panel with two passes of a 2 kg roller. The samples wereaged against the glass for 10 min at 23° C. or 24 h at 23° C. or in anoven at 85° C. for 24 h. The test was conducted on a slip/peel tester(Instrumentors Inc.; Strongsville, Ohio). The tape was removed from theplate at a peel angle of 180° and a platen speed of 90 inches per minute(2.288 m/min) for a total of 2 seconds. The force required to remove thetape was measured in grams per 0.5 inch and converted toNewtons/decimeter (N/dm). Results are the average of three tests on eachadhesive and shown in Tables 1 and 2.

Wet Out Test

A glass slide with dimensions of 3 inch×1 inch was held at an angle of69° and dropped on the self-wetting adhesive surface. The time to wetout the glass slide was recorded in seconds and divided by the area wetout (i.e. 3 in² for the glass slide). The test was performed three timesfor each sample, and the average was reported as shown in Tables 1 and2.

Examples 1-21

A syrup was prepared for examples 1-21 by adding 200 g, 1.08 mol of2-octyl acrylate (2-OA, provided by 3M Company, St. Paul, Minn.) and0.32 wt % Irgacure 651 (BASF, Florham Park, N.J.) in a clear quart jarand sparged with nitrogen for 15 minutes. The sample was then irradiatedwith ultraviolet light (Sylvania Blacklight 350 nm) for 30 seconds topartially polymerize the composition to a syrup polymer. Upon completionof the irradiation, the syrup polymer was bubbled with oxygen to stopthe polymerization for 30 seconds. The material was magnetically stirreduntil a homogenous mixture was achieved. From this syrup polymermaterial, 20 g aliquots were taken and placed in amber jars. HDDA,Coatosil 3509 and Irgacure 651 were added to the 20 g aliquots inamounts shown in Table 1. The material was rolled until a homogenousmixture was achieved.

Examples 21-42

The same procedure was used to prepare examples 21-42 except thatisooctyl acrylate was used rather than 2-octyl acrylate in the syrup.The formulations are shown in Table 2.

Coating of Self-Wetting Adhesives

After rolling, the syrup polymer compositions were knife coated onto thenon-primed side of a primed PET film (Mitsubishi Hostaphan™ 3SABPolyester Film, Mitsubishi Polyester Film Inc.; Greer, S.C.). The coatedadhesives were then cured by UVA light (˜350 mJ/cm²) and UVC light (˜70mJ/cm²). The cured adhesive had a thickness of about 2 mil (˜50micrometers).

TABLE 1 2-OA-based Formulations Peel Peel Peel (N/dm) (N/dm) (N/dm) HDDACoatosil 3509 Wet Out 10 min, 24 h, 24 h, Ex (wt %) (wt %) (s/in²) 23°C. 23° C. 85° C. 1 1.96 0.00 6.8 3.79 7.59 15.18  2 1.95 0.49 6.0 2.785.56 11.12  3 1.94 0.97 5.8 2.74 5.48 10.96  4 1.87 4.67 4.0 1.61 3.226.45 5 1.79 8.93 4.6 1.07 — — 6 1.71 12.82 4.4 0.55 — — 7 1.64 16.39 4.61.45 — — 8 4.76 0.00 8.5 1.29 1.76 1.12 9 4.74 0.47 3.9 1.26 1.04 1.2710 4.72 0.94 4.5 0.92 1.11 1.37 11 4.55 4.55 2.8 0.59 — 0.59 12 4.358.70 3.0 — — — 13 4.17 12.50 2.9 — — — 14 4.00 16.00 8.1 — — — 15 9.090.00 5.7 0.90 1.04 0.82 16 9.05 0.45 5.6 0.89 1.29 0.99 17 9.01 0.90 5.40.87 1.63 0.96 18 8.70 4.35 4.2 0.68 0.77 1.44 19 8.33 8.33 11.1 — — —20 8.00 12.00 11.5 — — — 21 7.69 15.38 6.1 — — —

TABLE 2 IOA-based formulations Peel Peel Peel (N/dm) (N/dm) (N/dm) HDDACoatosil 3509 Wet Out 10 min, 24 h, 24 h, Ex (wt %) (wt %) (s/in2) 23°C. 23° C. 85° C. 22 2 0 6.4 2.97 2.87 2.46 23 1.95 0.49 4.6 1.74 1.401.94 24 1.94 0.97 3.8 1.63 1.23 1.93 25 1.87 4.67 3.3 1.08 0.61 1.60 261.79 8.93 3.0 0.67 0.32 1.38 27 1.71 12.82 2.9 0.47 0.13 1.07 28 1.6416.39 3.8 0.37 0.16 0.91 29 4.76 0.00 4.1 1.15 1.10 0.96 30 4.74 0.474.0 0.82 0.64 0.84 31 4.72 0.94 5.3 0.74 0.54 0.86 32 4.55 4.55 3.4 0.590.25 0.90 33 4.35 8.70 3.2 0.44 0.25 0.78 34 4.17 12.50 2.8 0.29 0.080.68 35 4.00 16.00 3.3 — — — 36 9.09 0.00 5.0 0.66 0.76 0.66 37 9.050.45 4.7 0.56 0.38 0.64 38 9.01 0.90 6.0 0.45 0.47 0.63 39 8.70 4.35 3.90.47 0.25 0.53 40 8.33 8.33 3.3 — — — 41 8.00 12.00 2.8 — — — 42 7.6915.38 2.7 — — —

What is claimed is:
 1. A syrup polymer composition comprising: a) 5 to40 parts by weight of a low T_(g) (meth)acrylate solute copolymercomponent; b) 60 to 95 parts by weight of a low Tg solvent monomersolvent monomer component comprising low Tg monomers and amultifunctional acrylate; the sum of a) and b) being 100 parts byweight; c) 5 to 50 parts by weight, relative to a) and b) of a siloxanecopolymer having at least one polydiorganosiloxane segment and at leaston oxyalkylene segment relative to 100 parts a) and b).
 2. The syruppolymer composition of claim 1 wherein the composition comprises 5 to 20parts of siloxane copolymer, relative to 100 parts of a) and b).
 3. Thesyrup polymer composition of any of the previous claims wherein thesolute copolymer comprises: a) 95-100 parts by weight of low T_(g)monomer units; b) 0 to 5 parts of acid-functional monomer units; c) 0 to5 parts of a non-acid functional polar monomer the sum being 100 partsby weight.
 4. The syrup polymer composition of any of the previousclaims wherein the solvent monomer component comprises: a) 60 to 90parts by weight of low T_(g) monomers; b) 0 to 5 parts of acidfunctional monomers; c) 10 to 40 parts of a multiacrylate; the sum being100 parts by weight.
 5. The syrup polymer composition of any of theprevious claims comprising 20 to 50 parts of a siloxane copolymer,relative to 100 parts a) and b).
 6. The syrup polymer composition of anyof the previous claims wherein the solute low T_(g) copolymer comprises1 to 5 parts by weight of acid-functional monomer units and 5 to 95parts by weight of low T_(g) monomer units.
 7. The syrup polymercomposition of any of the previous claims wherein the solute low Tgcopolymer comprises 1 to 5 parts by weight of non-acid-functionalmonomer units.
 8. The syrup polymer composition of any of the previousclaims wherein the solvent monomer component comprises 1 to 5 parts byweight of acid-functional monomer units.
 9. The syrup polymercomposition of any of the previous claims wherein the solute low T_(g)copolymer comprises 100 parts by weight of low T_(g) monomer units. 10.The syrup polymer composition of any of the previous claims wherein thesolute low T_(g) copolymer has a T_(g) of less than 0° C., preferablyless than −20° C., more preferably less than −50° C.
 11. The syruppolymer composition of any of the previous claims wherein the segmentedsiloxane copolymer comprises at least two (meth)acrylate groups.
 12. Thesyrup polymer composition of any of claims 1-11 wherein the segmentedsiloxane copolymer is of the formula:X—(R²—O)_(a)—Q—(SiR¹ ₂O)_(b)—Q—(O—R²)_(a)—X where X is H or a freeradically polymerizable group; R² is an alkylene group; Q isdifunctional linking group; R¹ is alkyl or aryl group; and a and b areindependently integers greater than 1, with the proviso that at leastone X is a free radically polymerizable group.
 13. The syrup polymercomposition of any of claims 1-11 wherein the segmented siloxanecopolymer is of the formula:R¹ ₃SiO—(SiR¹ ₂O)_(b)—(SiR¹(—Q(—O—R²)_(a)—X)O)_(a)SiR¹ ₃ where R¹ isalkyl or aryl group; X is a free radically polymerizable group; R²is analkylene group; Q is a difunctional linking group; and a and b areindependently integers greater than
 1. 14. An adhesive comprising thecured syrup polymer composition of any of the previous claims.
 15. Amethod of making an adhesive comprising the steps of: partiallypolymerinzing a low T_(g) monomer and optional acid functional monomerto a viscosity produce a syrup polymer composition, adding amultifunctional acrylate crosslinker agent, optional additionalmonomers, and a siloxane copolymer having at least onepolydiorganosiloxane segment and at least on oxyalkylene segment, andfurther photopolymerizing.
 16. The method of claim 15 wherein the syruppolymer composition has a viscosity of from 500 to 10,000 cPs at 22° C.17. The method of any of claims 15-16, wherein the syrup copolymercomprises up to 30 parts by weight of the solute copolymer in solventmonomers.
 18. The method of any of claims 15-17 comprising the steps ofpartially polymerizing a low T_(g) monomer and other optional monomersto produce a syrup polymer composition of claim 1, adding amultifunctional acrylate crosslinker agent, additional monomers, andplasticizer, and further photopolymerizing.
 19. The method of any ofclaims 15-18 where the other optional additional monomers comprisenon-acid functional polar monomers.
 20. The method of claim 18 whereinup to 20 parts of additional monomers are added relative to 100 partstotal monomers.
 21. An adhesive article comprising a substrate and acoating of the cured adhesive of nay of claims 1-13 on a surfacethereof.
 22. The adhesive article of claim 21 wherein the adhesive has a180° peel value of ≦5 Newtons/decimeter.
 23. The adhesive article ofclaim 21 wherein the substrate is transparent.
 24. The adhesive articleof claim 21 wherein the adhesive has a transmissivity of greater than90% in the visible range.
 25. The adhesive article of claim 21 whereinthe substrate is a solar control film.
 26. The adhesive article of claim21 having a transmissivity of at least 80% in the visible range.
 27. Anadhesive comprising a) 10 to 40 parts by weight of a low T_(g)(meth)acrylate solute copolymer component; b) 60 to 90 parts by weightof a crosslinked low T_(g) solvent copolymer component; and c) 5 to 50parts by weight a siloxane copolymer having at least onepolydiorganosiloxane segment and at least on oxyalkylene segment,relative to a) and b).